clarification required regarding Channel.

Discussion in 'Wireless & RF Design' started by saraswathi.95, May 24, 2014.

  1. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    Hello,
    what physical properties of channel makes it to be called as time variant or invariant system?
    why do they offer different delays to different frequencies of signal?
    why do channels have non linear properties?
    Thank you.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Can you be more precise about what exactly you mean by a channel? I don't want to assume one thing when you might mean something else entirely.
     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Sounds like Homework.
     
  4. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    Channel can be coaxial cable or any other transmission medium related to communion systems
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    Let us start with an article on what time invariant systems are:
    http://en.wikipedia.org/wiki/Time-invariant_system

    I'm not familiar with any transmission medium (aka channel) that is time variant, so any further discussion of physical properties that might affect that is premature.

    Delay, or velocity of propagation, in a cable is a function of the arrangement of the conductors and the composition of the dielectric material between them. I know that the attenuation of a signal and its phase shift are functions of frequency. This is due to a cable looking like a distributed series inductance and distributed shunt capacitance. It is essentially a low pass filter.
    http://en.wikipedia.org/wiki/Transmission_line

    What non-linear properties are you talking about?
     
  6. bertus

    Administrator

    Apr 5, 2008
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    saraswathi.95 likes this.
  7. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    non linear property is output collected is not proportional to transmitted signal levels
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    Can you cite an example of where this might be the case?
     
  9. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    when i was reading about wave guides in microwave communications i have noticed it.
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    Waveguides, is unfortunately one area where I have limited familiarity. My RF experience is confined to the area of the spectrum that microwave engineers refer to as "nervous DC".

    The only insight I have is that solutions to the PDE for a particular waveguide have a great deal to do with the boundary conditions.
     
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